5-chapter 2 - Chapter 2: The Integumentary System Purpose...

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Chapter 2: The Integumentary System Purpose Understand the basic structure and functions of the integument. Become familiar with derivatives of the skin from representative clades. Understand the evolution of the skin in a phylogenetic context. Introduction (Ch. 2 Supplement- Figs. 2-2, 2-5, 2-12, 2-13) The skin or integument is a polyfunctional structure that plays many roles in craniates. It serves as the outside boundary layer between an organism’s internal and external environments. It is composed of many different tissue types and contains various structures ranging from blood vessels to nerves. The skin performs many functions, including: providing protection of and support for internal organs , modulating exchange and transport of salts , ions , gases , and water , serving as a receptor for pain and temperature , functioning in temperature regulation , serving as the basis for coloration which can act as camouflage or as a warning , and lastly it is its own complex ecosystem of viruses, bacteria, fungi, yeasts, mites, and other arthropods. Despite the multifunctional role that the skin plays, its basic structure and development are conserved among craniates. It is composed of three main layers: epidermis , dermis, and hypodermis (Figures 2-1, below, and supplementary figure 2-2). The epidermis is the outermost layer and is composed of epithelial cells that are derived from ectoderm. The epidermis rests upon a delicate layer of fibrils termed the basal lamina . The dermis is located beneath the epidermis and the basal lamina and is composed mainly of fibrous connective tissue derived developmentally from mesenchymal cells. This layer contains glands and hair. The dermis is often much thicker than the epidermis but contains far fewer cells. The hypodermis contains subcutaneous tissues including fat, connective tissue, blood vessels, and nerves. Fig. 2-1 . Typical sections of vertebrate skin showing major divisions of layers. ( Adapted from Liem et al. 2001 )
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The dermis and epidermis can be further subdivided based on the composition and fate of their various cell types. Just above the basal lamina lies a subdivision of the epidermis which is composed of one or two layers of basal stem cells, termed the stratum germinativum (Figure 2-1 above). These cells continually multiply and differentiate, providing the means by which vertebrate epidermis is continually renewed, even following injury. As these cells multiply they migrate towards the surface where they eventually slough off either individually or in sheets. In terrestrial vertebrates this outer layer of dead cells forms the stratum corneum located on the skin surface. Cells in this layer and other epidermal cells have the capacity to produce a water-insoluble protein
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5-chapter 2 - Chapter 2: The Integumentary System Purpose...

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